1. Field of the Invention
The present invention relates to a circuit breaker with a rebound preventer, and particularly, to a circuit breaker having a mechanism for preventing rebound upon a trip operation of the circuit breaker for protecting a circuit from over-current or short circuit.
2. Background of the Invention
A circuit breaker is an electric device installed on an electric circuit for safely blocking current to protect power systems and power equipment when the circuit is forcibly open or closed in a normally used state or when a fault current such as earth fault current or short circuit current. Typically, a circuit part of the circuit breaker may be provided with a spring and a rigid body, so as to enable fast operation upon opening a circuit. A trip mechanism of the circuit breaker is partially shown in FIGS. 1 and 2.
FIG. 1 is a side view showing a side surface of part of the trip mechanism, and FIG. 2 is a font view thereof. As shown in FIGS. 1 and 2, the circuit breaker 10 may include a movable contact 12 disposed therein. The movable contact 12 may be contactable with or separated from a fixed contact which is not shown so as to perform a trip operation. A push rod 14 formed of an insulating material may be connected to an end portion of the movable contact 12, and another end portion of the push rod 14 may be connected to an end portion of a main shaft 18 by interposing a contact spring 16 therebetween.
The main shaft 18 may be rotatably disposed based upon a rotation shaft 20, and a trip spring 22 may be connected near another end portion of the main shaft 18. The trip spring 22 and the contact spring 16 may serve to rotate the main shaft 18 in a clockwise direction in FIG. 1 upon a trip operation.
In the meantime, the rotation of the main shaft 18 is restricted within a prescribed range by a damping element. The another end portion of the main shaft 18 is connected to a rotation link 26 via a rod 24, and the rotation of the rotation link 26 is restricted within a prescribed range by a stop block 28. Therefore, when the main shaft 18 is rotated in a clockwise direction, the rod 24 is moved upwardly in FIG. 2. Accordingly, the rotation link 26 is rotated in a counterclockwise direction, and then stopped by the stop block 28.
However, actually, the rotation link 26 is crushed against the stop block 28 by a repulsive force, for example, to be thereafter moved in an opposite direction. Accordingly, an interval (gap) between the movable contact 12 and the fixed contact becomes narrower, which is referred to as ‘rebound.’ Such rebound is repeated plural times with gradually decreasing amplitude thereof. Consequently, insulation between poles cannot be maintained, resulting in an incomplete trip operation.
To avoid such problem, the stop block 28 is provided with an oil dash pot, accordingly the rebound can be decreased by an attenuation of the oil dash pot. The oil dash pot uses the attenuation due to oil contained therein. However, when a small amount of oil is contained, such oil can absorb a great impact but an excessively long time is required until the impact is attenuated. On the other hand, when a large amount oil is contained, the rebound quantity is increased. That is, as shown in FIG. 3, it can be noticed that for a small amount of oil, a relatively short time is spent until vibration due to the rebound is completely attenuated but an amount of strokes is increased. It can also be noticed that for a large amount of oil, the amount of strokes is decreased but time required until the vibration due to the rebound is completely attenuated is lengthened (see FIG. 4).
Furthermore, since an amount of impact adsorbed by the oil dash pot is not constant, the rebound quantity cannot be controlled as a designer wants to. Also, as time elapses, the property of the oil dash pot is changed due to oil is leakage or the like. In addition, if the circuit breaker becomes larger in size as currently does, an amount of impact occurred upon the trip operation is also increased. Accordingly, the oil dash pot has to become larger in size, but there is limitation of the size due to economical and spatial limits.